This invention relates to building sheets suitable for roofing and siding of buildings, and particularly to improvements in design of the overlapping portions of such building sheets.
Overlapping the flat planar edges of adjacent building sheets may form a tight seal, but the contiguous flat surfaces would encourage capillary attraction when the outside surface became wet, thereby passing the water through the joint to the inside surface. Typically, prior art lap joint constructions for such building sheets discourage capillary attraction at the overlap by spacing a portion of the overlapping sheet away from the lapped sheet to create an antisiphon gap. This widely-used technique is shown in U.S. Letters Patent Nos. 1,072,508, 1,444,170, 1,889,784, 2,153,119, 2,199,924, 3,481,094, 3,520,100, 3,906,696, and 3,990,206. Because such building sheets are typically formed with parallel ribs or corrugations to increase their strength and encourage draining, the structural components to form the antisiphon gap are usually incorporated into the ribbed or corrugated pattern.
Many of these lap joint constructions such as those taught in U.S. Letters Patent Nos. 1,072,508, 2,153,119, and 3,481,094 employ a complex design and consequently use a greater quantity of material to achieve the antisiphon lap than would a simple design. Since most of these building sheets are manufactured by rolling sheet steel through dies which form the sheet into the typically ribbed or corrugated patterns, a complex rib design not only uses more of the width of the original sheet of steel than a simpler rib design would, but also requires more elaborate dies and slower rolling speed. However, the complex lap designs do have the advantage of adding strength to the edges which discourages deformation during handling, transport and installation.
Several techniques of sealing the overlap are disclosed by the above-listed prior art patents. The simplest technique is embodied in U.S. Letters Patent Nos. 3,520,100 and 1,889,784 where the seal is achieved by having the shape of the overlapping portion generally conform to the shape of the lapped portion except for the provision of an antisiphon gap. This group of art does not disclose the use of a fastener to enhance or achieve this seal.
A widely used technique discloses the use of a fastener through the raised rib to achieve a positive seal by forcing the contiguous surfaces of the lap joint together or by concentrating pressure at one or more points within the lap joint as disclosed in U.S. Letters Patent Nos. 1,444,170, 1,072,508, 2,153,119, 2,199,924, and 3,990,206. This technique, while effective to achieve a positive seal, has several problems associated with it. Use of a sealing washer or packing is necessary to assure that water does not enter into the antisiphon lap joint from around the fastener. The fastener therefore must be emplaced with sufficient force to compress a rubber or neoprene washer customarily used to form a watertight seal around the fastener. Fastening through the raised rib of the lap joint with sufficient force to compress the washer can distort the rib by either denting or battering. This distortion can effect the seal between the lapped and overlapping portions or interfere with the antisiphon gap. Of course, the rib or raised portion of the lap joint may be strengthened by employing a more complex cross-sectional design or by using heavier gauge material in the building sheet, but these solutions increase the manufacturing costs. Since these building sheets are customarily made of steel or other metal, another problem with this method of sealing relates to the relative movement of the metal resulting from various causes. When the fastener is emplaced through the rib rather than flush on the major planar surface of the sheet, the effect of the metal expanding and contracting due to changes in temperature is magnified by the lever arm provided by the unsupported shaft of the fastener. This movement as well as other movements of the sheeting due to wind, weather, settling of the underlying structure, and the like are more likely to gradually loosen a fastener placed through a rib than one which is snugly emplaced through a planar portion of the sheet with no exposed shaft.
A third type of seal disclosed in U.S. Letters Patent No. 3,990,206 avoids the above-mentioned problems associated with fastening through the rib by placing the fastener off the rib but still using the force of the fastener to enhance the seal. This is accomplished by configuring the overlapping portion so that the extreme edge would project below the plane of the building sheet and is resiliently distorted by the force of the fastener to sit flush on the plane of the underlying sheet. However, a large percentage of the overlapping portion remains in contact with the lapped portion and because of this large area of mutual contact present in this lap joint, the force of the fastener is somewhat distributed and not focused at the sealing edge.